linux-kernel - [PATCH] PCI/sysfs: add write attribute for boot

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Date:   Sun, 26 Sep 2021 15:15:39 +0800
From:   Zhenneng Li <lizhenneng@...inos.cn>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zhenneng Li <lizhenneng@...inos.cn>
Subject: [PATCH] PCI/sysfs: add write attribute for boot_vga

Add writing attribute for boot_vga sys node,
so we can config default video display
output dynamically when there are two video
cards on a machine.

Xorg server will determine running on which
video card based on boot_vga node's value.

Signed-off-by: Zhenneng Li <lizhenneng@...inos.cn>
---
 drivers/pci/pci-sysfs.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 7bbf2673c7f2..a6ba19ce7adb 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -664,7 +664,29 @@ static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr,
 			  !!(pdev->resource[PCI_ROM_RESOURCE].flags &
 			     IORESOURCE_ROM_SHADOW));
 }
-static DEVICE_ATTR_RO(boot_vga);
+
+static ssize_t boot_vga_store(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	unsigned long val;
+	struct pci_dev *pdev = to_pci_dev(dev);
+	struct pci_dev *vga_dev = vga_default_device();
+
+	if (kstrtoul(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	if (val != 1)
+		return -EINVAL;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (pdev != vga_dev)
+		vga_set_default_device(pdev);
+
+	return count;
+}
+static DEVICE_ATTR_RW(boot_vga);
 
 static ssize_t pci_read_config(struct file *filp, struct kobject *kobj,
 			       struct bin_attribute *bin_attr, char *buf,
-- 
2.25.1


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